Plastic tubing made of PVC.TM. or the like is widely used in many industries. Some of the uses of plastic tubing require it to be closed off or sealed at one or both ends. Raw tubing which is sealed at both ends can be a very inexpensive way to form a container for all sorts of materials in all sorts of applications. This is especially true if re-opening of the tube is not required, thereby permitting a permanent heat or weld seal to be used instead of a threaded end fitting, or the like.
One such application wherein heat or weld seals are well suited is in the manufacture of cylindrical elements for a heat sink as used in a solar energy furnace. These cylindrical elements are permanently sealed at both ends, with a suitable chemical, such as calcium chloride solution contained therein for absorbing and storing heat for later use. Depending on the capacity of the furnace, the heat sink might require a large number of cylinders of a similar size and length. As can be appreciated, this is an application which would be particularly suited to some type of automatic operation in making these cylinders out of raw plastic pipe.
In the prior art, sealing and filling these cylinders and other applications which have required closing off or sealing plastic tubes have been accomplished by hand using somewhat crude techniques. For example, a blow torch or the like may be used to heat and soften an end of a tube and a clamp may then be tightened down on the end of the tube to weld it and create a seal. As can be appreciated, there are many problems using this approach including ignition of the plastic tube or its contents, over-heating causing cracks and leaks in the areas adjacent the seal, injury to the operator caused by accidental contact with either the blow torch, the clamp, or the hot plastic tube, and the increased expense of any hand operation including high labor costs, wasted materials, and reliance on the skill of the worker in achieving satisfactory results.
To solve these and other problems, applicant has succeeded in designing and developing a machine and a method for automatically hot weld sealing the ends of raw thermoplastic tubing, such as that made of polyvinyl chloride or the like. For those applications requiring the tube to be filled with a fluid material, such as in the heat sink application, applicant's device also has the capability of automatically filling the tube once an end has been weld sealed. To enhance the weld seal formed automatically by the machine, it also has the capability of roughening or abrading the inner surface of the tube end which removes any film of oil or the like from the surface and also increases the bonding between the surfaces as it is weld sealed. With the prior art method of hand sealing, this abrading step is often neglected because of the increased time and expense involved to perform this extra step by hand.
Applicant's machine is automated, so that once an operator places a length of raw tubing into the machine and clamps it in place, the machine automatically takes over and abrades the inner surface of the tube end, lowers a heating head into the tube end to heat it from the inside out and, after the tube end has been heated sufficiently, retracts the heating head and then collapses the tube end by simultaneously actuating four air cylinders with plows and guide legs which converge radially inward against it. The plows are held sufficiently long to weld the collapsed tube end as it cools and the pressure of the plows ensures a solid weld between the sidewalls of the tube. At the end of the cycle, the tube may be removed from the machine, turned over, and placed back in the machine to automatically start the second half of the cycle. During the second half of the cycle, the tube is automatically filled by a fill arm before the second end is sealed by the same method. At the end of the second half of the cycle, a completed cylinder filled with the fluid material, such as calcium chloride solution, has been automatically formed and the machine is ready to accept another raw tube for processing.
Applicant's machine is designed to provide many advantages over the prior art. For example, the heating head assembly may be quickly disconnected and removed from the machine and a replacement assembly inserted to permit continuous operation should the heating head fail for any reason. While it is not expected that replacement of the heating head assembly due to failure would be required very often, this one component is virtually the only component expected to fail because of the heat rods contained therein. Furthermore, it is often desirable to change the temperature to accommodate tubing made of different plastic materials. With this design, applicant's machine is readily changed over to provide this different operating temperature.
Applicant's machine also provides other advantages and features including adjustability for different height tubing, separate bottom plates to positively receive and hold either a raw or sealed end, fully adjustable timed heating, filling, and welding by the plow assembly, alternately measuring the fill by sensing the weight of the tube, pressurized air cooling of the heating head assembly with improved insulated mounting to avoid heat transfer from the head to the rest of the machine, a free floating stripping plate to ensure reliable retraction of the heating head from the heated tube, a guide ring to center the carriage assembly on the tube end and a tube straightener and holder to prevent misalignment of the tube, and full adjustability of the operating parameters of the machine to provide for changeover as is necessary to process tubing made of different plastics or of different sizes and lengths. These and other advantages of applicant's device are more fully explained in the drawings and description of the preferred embodiment which follows.